As known, a polarized lens is widely adopted for sunglasses, goggles and so forth, which lens is conventionally sandwiched between two pieces of lenses (refer to page 3 through 5 and FIG. 1 through FIG. 3 of Japanese Patent Application Laid-open No.7-350122).
Also, nowadays, in light of the streamlining of the spectacles' structure and safety in case of the lens being broken during use, the mainstream structure of which is arranged by integrally laying a polarized lens over a plastic lens.
Such plastic polarized lens as mentioned above is produced by disposing a polarized film on a molding surface of a casting die and injecting a fused casting resin into such die so as to mold the same polarized lens. However, this production method is encountered with problems wherein a polarized film experiencing a high-temperature thermal history from a fused molding resin is distorted and the fluid resistance of the fused resin during injection shifts the polarized film within the casting die so as to make it difficult to stabilize the direction of a polarized axis to a given position.
Further, in case of injection molding of plastic resin material, the imbalance of the internal pressure of the casting die and the curing speed of the casting resin locally cause inconsistency in density and distortion to a molded product, which is likely to bring about defects in optical anisotropy and so forth.
In view of the inconveniences encountered with the prior art as mentioned above, the present invention is to provide a method of producing a polarized lens which allows a polarized film to be securely positioned within a casting die and a polarized lens to be cast in a uniform density and be almost free from any distortion on the surface so as to secure the stable uniformity of a lens as produced and a casting die used in the same method.